Only inherit the session ID context in SSL_set_SSL_CTX if the existing

context was also inherited (matches that of the existing SSL_CTX).
Reviewed-by: NTim Hudson <tjh@openssl.org>

ssl/ssl_lib.c

@@ -3191,24 +3191,31 @@ SSL_CTX *SSL_set_SSL_CTX(SSL *ssl, SSL_CTX* ctx)
 			}
 		ssl_cert_free(ocert);
 		}
-	CRYPTO_add(&ctx->references,1,CRYPTO_LOCK_SSL_CTX);
-	if (ssl->ctx != NULL)
-		SSL_CTX_free(ssl->ctx); /* decrement reference count */
-	ssl->ctx = ctx;
 
-	/*
-	 * Inherit the session ID context as it is typically set from the
-	 * parent SSL_CTX, and can vary with the CTX.
-	 * Note that per-SSL SSL_set_session_id_context() will not persist
-	 * if called before SSL_set_SSL_CTX.
-	 */
-	ssl->sid_ctx_length = ctx->sid_ctx_length;
 	/*
 	 * Program invariant: |sid_ctx| has fixed size (SSL_MAX_SID_CTX_LENGTH),
 	 * so setter APIs must prevent invalid lengths from entering the system.
 	 */
-	OPENSSL_assert(ssl->sid_ctx_length <= sizeof ssl->sid_ctx);
-	memcpy(&ssl->sid_ctx, &ctx->sid_ctx, sizeof(ssl->sid_ctx));
+	OPENSSL_assert(ssl->sid_ctx_length <= sizeof(ssl->sid_ctx));
+
+	/*
+	 * If the session ID context matches that of the parent SSL_CTX,
+	 * inherit it from the new SSL_CTX as well. If however the context does
+	 * not match (i.e., it was set per-ssl with SSL_set_session_id_context),
+	 * leave it unchanged.
+	 */
+	if ((ssl->ctx != NULL) &&
+		(ssl->sid_ctx_length == ssl->ctx->sid_ctx_length) &&
+		(memcmp(ssl->sid_ctx, ssl->ctx->sid_ctx, ssl->sid_ctx_length) == 0))
+		{
+		ssl->sid_ctx_length = ctx->sid_ctx_length;
+		memcpy(&ssl->sid_ctx, &ctx->sid_ctx, sizeof(ssl->sid_ctx));
+		}
+
+	CRYPTO_add(&ctx->references,1,CRYPTO_LOCK_SSL_CTX);
+	if (ssl->ctx != NULL)
+		SSL_CTX_free(ssl->ctx); /* decrement reference count */
+	ssl->ctx = ctx;
 
 	return(ssl->ctx);
 	}